The present invention generally relates to a Global Positioning System (GPS) receiver and more particularly to recalibration of a GPS receiver.
GPS receivers have local oscillators or oscillators that are used in a heterodyne or superheterodyne configuration for acquiring GPS satellite signals. The center frequency of the oscillator is typically determined by a controller, which uses a control signal calibrated to produce an oscillator output signal with an appropriate frequency for acquisition of one or more GPS satellite signals. GPS receivers generally search a window (e.g., +/xe2x88x9280 Hertz (Hz)) or band of frequencies centered on the center frequency.
Typically, a GPS receiver recalibrates the relationship between the control signal and the oscillator output signal each time the receiver successfully acquires a three-dimensional (3-D) position fix. Acquiring a 3-D position fix generally includes acquiring GPS satellite signals from four (4) GPS satellites. Therefore, acquisition of a 3-D position fix is an acceptable indicator that the frequency of the oscillator output signal is correct and also that the control signal producing the frequency of the oscillator output signal is correct.
Some Global Positioning System (GPS) receivers are unused for substantial periods. For example, GPS receivers used in search and rescue operations, humanitarian missions, or stored in warehouses or on store shelves can go months or even years before use. During these idle periods, aging of the oscillator can cause the frequency of the oscillator to drift. When the oscillator drifts, the control signal that once produced the correct oscillator center frequency will produce a different oscillator center frequency and the window may no longer include the frequencies for acquiring GPS satellite signals. Consequently, the GPS receiver may be unable to acquire one or more of the GPS satellite signals. To correct this problem, GPS receivers must be taken out of service to undergo a calibration procedure at a depot or factory. Also, GPS receivers have a limited shelf-life because of oscillator drift. The limited shelf-life further increases costs, complicates logistics, and degrades reliability of GPS receivers.
Accordingly, it is desirable to provide a GPS receiver with recalibration that addresses one or more of the foregoing problems and other problems not expressly discussed in this background. In addition, it is desirable to provide methods of recalibrating a GPS receiver and methods for reconfiguring a GPS receiver for recalibration. Furthermore, it is desirable to provide a program product that can be used by a GPS receiver for recalibration or uploaded during the reconfiguring of a GPS receiver. Moreover, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
A method for recalibrating a global positioning system (GPS) receiver is provided in accordance with an exemplary embodiment of the present invention. The method includes applying a first control signal to an oscillator for generation of an oscillator signal having an initial frequency and determining if an indicator of correct oscillator output frequency is present at the initial frequency. If an indicator of correct oscillator output frequency is not present, then iterative steps are followed until an indicator of correct oscillator output frequency is found. The iterative steps include: applying a new adjusted control signal to the oscillator for generation of a new frequency; determining whether an indicator of correct oscillator frequency is present; and if an indicator of correct oscillator output frequency is present with the oscillator having the new frequency, storing said adjusted control signal. If an indicator of correct oscillator frequency is present with the oscillator output signal having said initial frequency, then the initial control signal is stored.
A GPS receiver is also provided in accordance with the present invention. The GPS receiver includes an oscillator configured to generate an oscillator output signal, a mixer that is configured to receive an RF signal and convert that RF signal to at least one acquired GPS satellite signal using the oscillator output signal; and a controller coupled to said oscillator and to said mixer, said controller configured to implement a method including applying a first control signal to an oscillator for generation of an oscillator signal having an initial frequency and determining if an indicator of correct oscillator output frequency is present at the initial frequency. If an indicator of correct oscillator output frequency is not present, then iterative steps are followed until an indicator of correct oscillator output frequency is found. The iterative steps include: applying a new adjusted control signal to the oscillator for generation of a new frequency; determining whether an indicator of correct oscillator frequency is present; and if an indicator of correct oscillator output frequency is present with the oscillator having the new frequency, storing said adjusted control signal. If an indicator of correct oscillator frequency is present with the oscillator output signal having said initial frequency, then said initial control signal is stored.
In addition to the GPS receiver and the method for recalibrating a GPS receiver, a program product is provided in accordance with an exemplary embodiment of the present invention. The program product includes recalibration software executable in the processor of a GPS receiver for applying a first control signal to an oscillator for generation of an oscillator signal having an initial frequency and determining if an indicator of correct oscillator output frequency is present at the initial frequency. If an indicator of correct oscillator output frequency is not present, then iterative steps are followed until an indicator of correct oscillator output frequency is found. The iterative steps include: applying a new adjusted control signal to the oscillator for generation of a new frequency; determining whether an indicator of correct oscillator frequency is present; and if an indicator of correct oscillator output frequency is present with the oscillator having the new frequency, storing said adjusted control signal. If an indicator of correct oscillator frequency is present with the oscillator output signal having said initial frequency, then the initial control signal is stored. The program product also includes signal-bearing media bearing said recalibration software.
Furthermore, a method of reconfiguring a GPS receiver for recalibration is provided in accordance with an exemplary embodiment of the present invention. The method includes uploading a program into a memory of the GPS receiver that is executable by a processor of the GPS receiver. The program comprises recalibration software executable in the processor for applying a first control signal to an oscillator for generation of an oscillator signal having an initial frequency and determining if an indicator of correct oscillator output frequency is present at the initial frequency. If an indicator of correct oscillator output frequency is not present, then iterative steps are followed until an indicator of correct oscillator output frequency is found. The iterative steps include: applying a new adjusted control signal to the oscillator for generation of a new frequency; determining whether an indicator of correct oscillator frequency is present; and if an indicator of correct oscillator output frequency is present with the oscillator having the new frequency, storing said adjusted control signal. If an indicator of correct oscillator frequency is present with the oscillator output signal having said initial frequency, then the initial control signal is stored.